1. Field of the Invention
The present invention relates to radio frequency wireless systems that interconnect between an earpiece unit and a remote processing unit.
2. State of the Art
Recently, the usefulness of a device having a small earpiece unit capable of uplink and downlink wireless communication to a remote processing unit (RPU) has been realized. Such systems can be used as hearing aids or other communication devices. Audio data is transferred in a downlink connection between the earpiece unit and the remote processing unit and in an uplink connection between the remote processing unit and the earpiece unit. Such units can be part of a short-range body-worn network (Body LAN).
Typically, a radio frequency signal is used for the uplink and downlink connections. Since the downlink signal from the earpiece is in the radio frequency range, typically, the earpiece contains a radio frequency oscillator. Useful radio frequency oscillators are bulky and require a relatively large amount of power which can result in a battery too large for the earpiece unit. Furthermore, when a radio frequency oscillator is used in the earpiece unit, there can be discrepancies between the frequencies of the radio frequency oscillator in the remote processing unit and the earpiece unit. Such discrepancies can be the result of frequency drift or manufacturing differences in the radio frequency oscillators.
One way to remove the need for the radio frequency oscillator in the earpiece unit is to use the radio frequency energy of a unmodulated portion of an uplink signal to power a modulated downlink signal. An example of such a reflected power system is described in Anderson, U.S. Pat. No. 5,721,783. A radio frequency oscillator in the earpiece unit is not required because frequency of the unmodulated portion of the uplink signal is used for the downlink signal. The problem with such a reflected energy system is that there is typically not enough power in the downlink signal. For example, one prototype system produced to test such a reflective system had about a 50 dB shortfall in power for a reliable downlink connection. Thus, the reflected energy system either requires that the uplink power be very high or that the remote processing unit be able to detect a very weak downlink signal.
It is desired to have an improved system that does not use a radio frequency oscillator in the earpiece unit in order to reduce the required power and size of the earpiece.
The present invention generally relates to the use of a delay element such that frequency information from the uplink signal received in an uplink signal receiving period can be used for the transmitted signal sent in a later downlink transmitting period.
The use of a delay allows for the transmitted signal to be amplified. Simply amplifying the received signal without using a delay will result in undesirable feedback oscillations. Additionally, the use of the delay means that an unmodulated portion of uplink signal need not be sent to the earpiece unit during the downlink transmitting period. This will reduce the interference between the uplink and downlink signals.
A delay device that maintains the frequency information of RF signals is needed for use as the delay element of the present invention. An example of a delay element for radio frequency signals that can be used with the present invention is a surface acoustic wave (SAW) device. Surface acoustic wave devices convert input electrical signals into surface acoustic wave signals which take a given amount of time to transfer through the surface acoustic wave device. The output of the surface acoustic wave device is an electrical signal re-converted from the surface acoustic wave.
The surface acoustic wave devices can be designed to act as a relatively narrow bandpass filter at the desired frequency. In this way, undesirable signals at nearby frequencies received by the antenna are filtered away before the frequency information is used in a downlink signal.
A variety of modulation schemes can be used. In one embodiment of the present invention, the modulation of the downlink information is done using pulse position modulation (PPM). Two different delays are preferably used. One delay indicates a logical xe2x80x9czeroxe2x80x9d and the other delay indicates a logical xe2x80x9conexe2x80x9d. This can be implemented using a commercially available two output surface acoustic wave device.
The advantage of the systems of the present invention is that no radio frequency oscillator need be used in the earpiece unit. This reduces the supply power and size of the earpiece unit. Additionally, the frequencies of the uplink and the downlink signals will be exactly matched even if there is any drift or manufacturing variation in the radio frequency oscillator for the uplink signal, since the frequency information from the uplink signal is used for the downlink signal. Further, an amplified rather than reflected signal can be used for the downlink signal, thus the downlink signal can be kept relatively strong without requiring an overly powerful uplink signal. In a preferred embodiment, the power of the uplink and downlink signals are comparable.